Field of the Invention
This invention pertains to redox water treatment methods. In particular it pertains to a redox water treatment method utilizing sulfurous acid to act either as an oxidizing or a reducing solution for water conditioning.
State of the Art
Numerous water treatment methods using sulfurous acid are known. Harmon et al, U.S. Pat. No. 7,566,400 issued Jul. 28, 2009 discloses a wastewater chemical/biological treatment method and apparatus for saline wastewater treatment generating biofuels. Harmon et al, U.S. Pat. No. 7,455,773 issued Nov. 25, 2008 discloses a package wastewater chemical/biological treatment plant recovery apparatus and method including soil SAR conditioning. Theodore, U.S. Pat. No. 7,416,668 issued Aug. 26, 2008 discloses a wastewater chemical/biological treatment plant recovery apparatus and method employing sulfurous acid disinfection of wastewater for subsequent biological treatment. Theodore, U.S. Pat. No. 7,563,372 issued Jul. 21, 2009 discloses a package dewatering wastewater treatment system and method including chemical/mechanical separation via drain bags and metal hydroxide removal via lime precipitation. Theodore, U.S. Pat. No. 7,429,329 issued Sep. 30, 2008 discloses a hybrid chemical/mechanical dewatering method and apparatus for sewage treatment plants employing sulfurous acid and alkalinization chemical treatment along with mechanical separation. Theodore et al, U.S. Pat. No. 7,967,990 issued Jun. 28, 2011 discloses a hybrid chemical/mechanical dewatering method for inactivating and removing pharmaceuticals and other contaminants from wastewater employing a sulfurous hybrid chemical/mechanical dewatering method for inactivating and removing pharmaceuticals and other contaminants from wastewater employing a sulfurous acid and lime acidification/alkalinization cycle, and an oxidation/reduction cycle to selectively precipitate, inactivate, and remove pharmaceuticals from wastewater. Gong et al., U.S. Pat. No. 7,967,989 issued Jun. 28, 2011 discloses a groundwater recharging wastewater disposal method and apparatus using sulfurous acid acidification to enhance soil aquifer treatment. Harmon et al., U.S. Pat. No. 7,867,398 issued Jan. 11, 2011 discloses a method and apparatus to reduce wastewater treatment plant footprints and costs by employing vacuum recovery of surplus sulfur dioxide, Theodore (US20080314827) (Theodore '827) adds an oxidizing agent to oxidize chemical species before sulfur dioxide injection. It does not alter the states of the sulfur dioxide itself. Nor does Theodore '827 disclose continuous ORP and DO monitoring of acidified wastewater biological solutions to control and alter their ORP and DO to form oxic and anoxic solutions to promote biological growth in a biological reactor for nitrogen reduction.
FRWA's Training (Method of Controlling Nitrogen) (FRWA) FRWA discloses monitoring of ORP levels, but it does not disclose controlling and solely using sulfurous acid to produce oxidation and reduction solutions conducive to promote bacterial growth in a bioreactor.
The above methods all use sulfurous acid and are therefore dependent upon the sulfur dioxide, sulfite, and bisulfite concentrations in solution and the oxidation/reduction potential of a desired reaction. Sulfurous acid behaves as both an oxidizing and reducing agent, see J. Am. Chem. Soc., 1929, 51 (5) pp 1409-1428, “The Potential of Inert Electrodes in Solutions of Sulfurous Acid and Its Behavior as an Oxidizing and Reducing Agent” by Arthur A. Noyes, Harold H. Steinour. Consequently, where the waters to be treated vary in nutrient composition, alkaline and saline ionic concentrations, or require biological treatment requiring either a pre-treatment conditioning reducing agent or oxidizing agent, there remains a need for a method to regulate the electrical reduction potential of the sulfurous acid solutions. The method described below provides such a pre-treatment method.